Mechanism Research and Identification Method of Low Resistivity Gas Layers in the M block of Algeria

Abstract The M block in Algeria is located in the southern Sahara platform, with oil and gas reservoirs mainly composed of river-glacial marine facies, fluvial and shallow marine fine sandstones. The pore structure is complex, and the difference in resistivity logging between gas layers and water layers is not significant, resulting in difficulties in identifying and evaluating hydrocarbon zone and the occurrence of reservoir omission. Based on geological, mud logging, core experimental data, logging, formation water analysis and testing data together, the formation mechanism of low resistivity hydrocarbon zone and the response characteristics of logging curves were generalised. The research suggests that the main factors causing low resistivity in this area are strong heterogeneity, high formation water salinity, high shale content, etc. On this basis, in response to the difficulty of identifying low resistivity gas layers, three methods of assessment were constructed: resistivity reduction rate factor method, porosity curve differentiation technique method and double porosity overlap method, which can quickly identify low resistivity gas layers. The oil testing results have verified that this method significantly improves the interpretation accuracy, with a 17.2% increase in accuracy and good results. The test results show that the method can greatly improve the interpretation accuracy with current accuracy 89.1% and the method turns out to be effective. Based on the above methods, the distribution law of low resistivity oil and gas layers in the study area has been clarified, and favorable zones have been discovered, providing strong technical support for increasing reserves and production in the area.